LANDFILL: The Little Landfill that Could

Anne Watson | Aug 01, 2002

Arizona's Chandler landfill is proving you don't need to be an 800-pound gorilla to sustain a landfill gas-to-energy (LFGTE) project.

A 66-acre municipal landfill that holds 2.1 million cubic yards of waste, operators originally believed the Chandler site would not be able to maintain a quality methane supply to offset the manpower and equipment costs required to generate electricity.

However, as early as 1993, when methane began to amass and migrate from the landfill, Manager Gerry Backhaus wanted to use the gas instead of burning it off. At the time, a flare and wells were installed because there was no nearby manufacturing plant that could purchase the methane. Additionally, the quantity and quality of gas was thought to be too small to justify an LFGTE investment.

Backhaus never lost sight of his idea. First, he tried to find analyzer equipment to keep accurate measurements, but he found that analyzer technology wasn't able to withstand tough landfill conditions. His second system, manufactured by San Diego-based Landfill Gas & Environmental Products Inc. (LFG&E), entailed a computerized methane monitoring system to help support small LFGTE projects.

Typically, a large landfill relies on a few dependable wells to supply gas at high enough methane levels to constantly keep generators running. A smaller landfill, on the other hand, requires more monitoring because gas wells must be open and shut to ensure that the appropriate gas quality and quantity is being dispensed sufficiently from each well.

The system now monitors information from clusters of wells at the Chandler Landfill, updating the main office's computers about levels of methane, oxygen carbon dioxide, carbon monoxide, gas temperature, vacuum and flow. The equipment automatically shuts down or opens the wells and flares in response to the data.

For example, if sensors indicate that temperatures are rising around a well and could trigger a fire, the well head opening will reduce or shut down to curb oxygen flow into the system.

This monitoring equipment, combined with higher methane levels as the landfill is expected to close in 2005, finally enabled Chandler to reconsider a LFGTE project. And when the Phoenix Valley's electrical utility, SRP, became interested in purchasing electricity from Chandler's landfill, the city purchased two generators with gas-cleaning devices, and the project was born.

The Chandler Landfill now produces 200 cubic feet of gas per minute and eventually will peak at 400 cubic feet. The monitoring equipment provides an even, quality methane flow of 100 cubic feet per minute, which should enable the two generators to run for at least 25 years.

To power the generators, Chandler's system needs to produce gas at a 40 percent to 45 percent methane per volume level. Some of the wells vary from 20 percent to 50 percent methane. Therefore, the system orders blowers on poorer-producing wells to shut down while drawing methane from richer wells.

Backhaus and a landfill technician help to monitor gas flows from the landfill's main office, or they can dial in from their home computers to make adjustments. By spring 2003, the system also will be upgraded so that technicians can use personal data assistants (PDAs) to make changes and receive emergency notices on their wireless phones. Local residents will have Internet access to landfill data at that time, too.

In addition to being beneficial for the environment, the savings in manpower hours because of the monitoring system have helped make the LFGTE project viable. Without the system, methane would have begun to build and migrate, and the landfill would have needed to hire two technicians to monitor the wells, to watch for gas migration and to make continual adjustments. The manpower costs would have totaled approximately $3 million during 30 years, Backhaus predicts.

But so far, the city has only made an initial investment of approximately $198,000, and the next monitoring equipment upgrade should only add $350,000 for the additional probes and trenching, sump pumps, and improvements to the gas collection system. Even with two Caterpillar engines and equipment to clean the incoming gas and regulate the outgoing electricity, the total LFGTE project costs are predicted to be $400,000.

Chandler's investment will look even more promising once electricity revenues are totaled. In the last two weeks of April, when SRP began paying Chandler, the rate of 3.5 cents per kilowatt of energy generated earned the city approximately $3,500.